dissolve app/ into repo root (D-056)

Single Flutter package at the repo root. All code, tests, assets,
and platform directories moved from app/ to root. Package renamed
from clide_app to clide — all imports rewritten. Merged pubspec
combines core (ffi) and app (flutter, yaml, xterm) dependencies.
Makefile simplified: no APP_PRESENT conditionals, no cd, no daemon
lifecycle. 317 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/builtin/claude_control/src/extension.dart

@@ -0,0 +1,23 @@
+import 'package:clide/extension/extension.dart';
+
+/// Tier-reserved stub. Will surface a sidebar tab with sub-tabs
+/// Settings / Skills / Agents / Hooks / MCP — `.claude/` as a
+/// first-class IDE surface. Orthogonal to pql; purely clide-internal.
+/// Commands: `claude.settings.open`, `claude.skills.new`,
+/// `claude.skills.edit`, `claude.agents.new`, `claude.agents.edit`,
+/// `claude.hooks.log`, `claude.mcp.status`.
+///
+/// Distinct from `builtin.claude`, which is reserved for Tier 1's
+/// "run Claude Code in a PTY pane."
+class ClaudeControlExtension extends ClideExtension {
+  @override
+  String get id => 'builtin.claude-control';
+  @override
+  String get title => 'Claude control';
+  @override
+  String get version => '0.0.0-stub';
+  @override
+  List<String> get dependsOn => const [];
+  @override
+  List<ContributionPoint> get contributions => const [];
+}